In the fluorescent lamp art, the so-called rapid-start type of fluorescent lamp system is quite common. Therein, the filaments of the lamps are preheated for a short period of time to protect them from damage which often occurs with a cold ignition type system. Thereafter, ignition of the lamps is effected and the filament preheating potentials are no longer necessary.
Recently, there has been considerable emphasis on apparatus and techniques for reducing the electrical energy consumed by fluorescent light systems. One known attempt to reduce electrical energy expenditure is set forth in U.S. Pat. No. 4,256,993 issued to Morton on Mar. 17, 1981. Therein, a normally-closed (N/C) switch is coupled to a filament of one of a pair of fluorescent lamps. The (N/C) switch is shunted by a power reducing capacitor and a power reducing circuit is employed to direct the coupling and decoupling of the lamp filament and an energizing source. In effect, energy from a source is directly applied to the filament of one of a pair of fluorescent lamps through a (N/C) switch for a time period sufficient to insure ignition of the lamps. Thereafter, the power reducing capacitor is series connected with the filament of the lamp and the filament winding or energy source. Thus, the N/C switch is energized to provide a power-reducing capacitor in series with the filament of the rapid-start fluorescent lamp after lamp ignition.
A somewhat similar result is obtained with the system set forth in U.S. Pat. No. 4,146,820 issued to Bessone et al on Mar. 27, 1979. Herein, a power reducing system includes a pair of N/O switches each shunted by a power reducing capacitor and coupled to one filament of a fluorescent lamp. A power reducing means energizes the switches to provide a direct connection to the filaments from an energizing source for a given period of time or until the lamp ionizes. Thereafter, the energy applied to the switches is removed, the switches open and a capacitor is inserted into each line intermediate the energy source and the fluorescent lamp filament.
Still another approach to the conservation of power in a rapid-start fluorescent system is set forth in U.S. Pat. No. 4,010,399 issued on Mar. 1, 1977 to Bessone et al. Therein, a triac and two voltage divider resistors form a solid state switch which is inserted in each filament circuit of a pair of fluorescent lamps. The triac provides a low resistance path for applying power to the lamp filaments until lamp ionization is effected. Thereafter, the voltage across the voltage divider of each switch cuts off the triac current flow to the filament.
Although each of the above-described techniques does provide an advantage and a reduction in energy consumption over other known apparatus, each does leave something to be desired. For example, Morton (993) employs a single N/C switch coupling one lamp filament to an energizing source and also inserts a capacitor in the circuit upon ionization of the lamp. However, the N/C switch requires a constant source of energy to maintain a desired operational condition, the inserted capacitor reduces the light available from the lamp and heater current is disconnected in but one of multiple filaments of the lamp system.
Also, Bessone et al (820) employs but a single switch to reduce the current applied to one filament upon ionization of the lamp. Unfortunately, heater current is applied to the remaining filaments which is deleterious to conservation. Moreover, the introduced power reducing capacitors cause a reduction in light output available from the lamps. Moreover, Bessone et al (399) necessitates a power loss in each filament circuit due to the incorporated resistors of the solid state switching devices. Accordingly, the above techniques are expensive of components and labor, are limited in so far as a reduction in filament heating is concerned or undesirably reduce the light output available from the lamps. Moreover, switches shunting capacitors must be of a relatively heavy-duty type in order to absorb the energy available from a fully loaded capacitor.